The invention relates to a wheel and axle assembly for securing a wheel in position on a material handling cart used for a material handling cart and rack system.
In industrial and heavy commercial duty applications such as material handling cart and storage rack systems, load-bearing wheels are routinely subjected to shocks and wear from repeated usage, sudden applications of heavy loads, and collisions with various objects. These conditions can both occur suddenly and gradually and can lead to the loosening or disconnection of cart wheels. When any one wheel on a given cart is loosened or becomes disconnected from the cart, both that cart and any other cart or carts associated with it may become inoperable and may need to be removed from service until a repair can be made. This may lead to the incurring of significant expenses for the operator due to the costs of repairs, down time, and the inaccessibility of stored items.
The development of improved cart and storage rack systems has also led to the development of efficient space-saving techniques for positioning multiple carts in confined or restricted spaces. For example, in the case of pushback storage rack systems, such as that disclosed in U.S. patent application Ser. No. 09/971,752 filed on Oct. 4, 2001, improvements in design have enabled significant increases in the numbers of wheeled storage rack carts that can be stacked for use in a single storage rack lane. Although such innovations have made it possible to significantly increase the number of available carts in a system, and have therefore increased the number of loads that can be stored in a restricted space, such innovations have also meant that more cart wheels must be accommodated in spaces that are no less restricted than in previous designs.
For this reason, it has become increasingly important that assemblies for mounting wheels on material handling carts be configured to occupy a minimum amount of space. However, it has become equally important that wheel assemblies be configured to minimize the likelihood that a cart wheel on any given cart will loosen or become disconnected, even when the wheel or cart is subjected to extreme operating conditions.
The invention is a wheel and axle assembly for a material handling cart in which a cart wheel is fastened into position with a bolt that is itself secured in place with an appropriate locking material. The wheel has an inner hole which extends through the wheel and which defines an inner wheel surface. A first bearing is positioned within the hole and has an outer race which engages the inner wheel surface and an inner race which rotates with respect to the outer race. A snap ring locks the first bearing in position within the inner hole of the wheel.
An axle extends through the bearing and has a rolled bearing engagement surface that engages the inner race of the bearing. The axle has a shoulder which has a greater axial radius than the bearing engagement surface and which contacts the bearing. The axle also has a rolled load bearing surface which connects the wheel and axle assembly to the cart or load. The axle has a bolt cavity that has female cavity threads within it and an inside tapered portion at one end of the female cavity threads. A bolt having male bolt threads and a head with an outside tapered portion engages the female cavity threads and can be screwed into the bolt cavity until the outside tapered portion of the bolt contacts the inside tapered portion of the bolt cavity. The head of the bolt has a head diameter that is greater than the inside diameter of the race of the bearing. Thus, when the head of the outside tapered portion of the bolt contacts the inside tapered portion of the bolt cavity, the head of the bolt engages the inner race to axially lock the bearing against the shoulder of the axle.
To prevent the bolt from disconnecting or loosening its engagement with the bolt cavity of the axle, a locking material is added to the male threads of the bolt. In some embodiments of the invention, the locking material can comprise a strip made of nylon or other resilient material that is inserted into a strip cavity located at or near the male threads of the bolt. In other embodiments of the invention, the locking material can comprise a chemical locking compound or other material applied directly to the surfaces of the male threads. The locking material secures the male threads of the bolt in engagement with the female threads of the bolt cavity so that the outside tapered portion of the bolt remains in contact with the inside tapered portion of the bolt cavity.
Those skilled in the art will realize that this invention is capable of embodiments which are different from those shown and that details of the structure of the wheel and axle assembly described herein can be changed in various manners without departing from the scope of this invention. Accordingly, the drawings and descriptions are to be regarded as including such equivalent wheel and axle assemblies as do not depart from the spirit and scope of this invention.